Batteries based on lithium (Li), such as lithium-ion batteries, are attractive due to their high energy density compared to other commercial batteries. Lithium-ion batteries are used commercially today in computers, cell phones, and related devices.
Lithium-based batteries (including lithium-ion, lithium-sulfur, and lithium-air systems) have significant potential in transportation applications, such as electric vehicles. For transportation-related applications, long cycle life is a requirement. Presently, this requirement has not been met.
Battery lifetime is often a critical factor in the marketplace, especially for commercial, military, and aerospace applications. Previous methods of extending battery life include employing long-life cathode and anode materials, and restricting battery operation to avoid conditions detrimental to battery life. Examples of such detrimental conditions include high and low temperatures, high depths of discharge, and high rates. These restrictions invariably lead to under-utilization of the battery, thus lowering its effective energy density. In addition, precise control of cell temperature with aggressive thermal management on the pack level is usually required, which adds significantly to system weight, volume, and cost.
A problem in the art associated with lithium-sulfur, lithium-air, and lithium-ion batteries is undesirable chemical migration that results in parasitic chemical reactions at the anode or cathode. For example, in batteries with manganese oxide and iron phosphate cathodes, dissolved metal ions often migrate to the anode where they are reduced and compromise the integrity of the solid electrolyte interface layer. Battery capacity degrades due to consumption of active ions. Battery storage and cycle life can be greatly improved if such undesirable chemical interactions are reduced or eliminated.
A successful battery separator layer should have a wide electrochemical stability window to be stable against the battery anode and cathode. In addition, the separator layer needs to have limited electronic conductivity in order to prevent electrical leakage between the two electrodes. When both requirements are imposed, the available materials are very limited and solid electrolyte is rarely free-standing.
In view of the foregoing shortcomings, new battery structures are needed to address important commercialization issues associated with lithium-sulfur, lithium-air, and lithium-ion batteries. For example, a relatively thin free-standing separator layer is a long-felt need in the art. Preferred battery structures would help prevent or eliminate battery failure due to eventual contamination during operation, thereby increasing battery lifetime and overall energy efficiency.